Lamp



Jan. 19, 1937.

T. W. ROLPH LAMP Filed Dec. 7, 1935 2 Shee-tsSheet l No brightness limit.

Valli/M m briyiw [l1 briqkzness limit.

4 r? a r" 39 Q; 75 bf Law bright: 95s limit. J5 35 m mini;

INVENTOR; THOMAS WROLPH A TTORNE Y.

T. W. ROLF-H Jan. 3.9, 13 337.

I LAMP Filed Dec.. 7, 1935 2 Sheets-$nee 2,

2 Feet from lamp axis A TTQRNEY.

Patented Jan. 19, 1931 N 111?. FFQ

man

Application December 2, 1935, Serial No. 53,356

13 Claims.

This invention relates to luminai-rs used for purposes of study and reading. Typically, the luminair is made for placement on a desk or table but it may also be supported or suspended in any other way.

Study and reading luminairs which act by simple difiusion of light do not give a sufficient spread for satisfactory working illumination. Such lamps may be made with white diffusing glass to transmit the light and with white reflecting shades to reflect it. Such materials diffuse light, sending it out in all directions, the emission from any point on the surface being in accordance with the well-known cosine law. The

ing material. These elements are combined in such a way that the illumination at a considerable distance from the lamp is obtained by means of the light-director and the illumination close to the lamp is obtained by means of the diffuse reflector. This combination has certain unique advantages both in illumination and in protection of the eyes from direct and reflected glare.

Other and further objects of the invention will appear as the description proceeds.

The accompanying drawings show, for purposes of illustrating the present invention, several embodiments in which the invention may take form, it being understood that the drawings are illustrative of the invention rather than limiting the same.

In these drawings:-.

Fig. 1 is a side elevational view of a lamp, parts being indicated in section;

Fig. 2 shows the light distribution or photometric curve given by the lamp shown in Fig. 1, together with the distribution given by each of two parts of the lamp; and atypical photometric curve for the downwardly directed light in a lamp employing a diffusing bowl;

Fig. 3 indicates the distribution of illumination on a desk from the complete lamp and from each of two parts of the lamp;

Fig. 4 shows a diagram of zones of permissible Fig. 5 shows a luminair in which the lower portion of the light director is a reflector instead of a refractor; and

Figs. 6 and 7 are vertical and horizontal sections through a further modified form of construction.

The study and reading lamp illustrated in Fig. 1 comprises a light source II with light cen- 'ter 12 supported by a stem 13 at suitable height. The stem also supports a light director 14 having two portions which may be integral or separate. The lower portion I5 is a refractor with annular prisms to condense the rays and distribute the light out over the desk through wide angles. The upper part l6 directs light to the ceiling and may be a prismatic reflector, as indicated in Fig. 1, or an opal reflector or an opaque reflector. Outside Ill of this light director and ordinarily supported by it, is a translucent shade ll of paper or parch- -ment finished white inside. This shades the eyes from view of the light director under ordinary conditions and also receives scattered light transmitted by the light director and delivers it in a diffused downward distribution of light, as indicated in the drawings. This diflusely reflecting shade ll may be made of other materials such as glass, fabric or metal. It may be translucent or opaque, but should always have a good reflecting surface inside.

Where the upper or reflecting part iii of the light director is a prismatic reflector, it allows a certain part of the light to pass through to the shade. However, as indicated above, this portion of the reflector may bemade of opaque material which will reflect light to the ceiling. In that case, the shade I! will be illuminated by means of' light transmitted through the refractor portion l5 and scattered from the main beam. Where the reflector part is made of diffusely reflecting glass, such as opal, it will also transmit a certain amount of light to the shade. Fig. 2 is a photometric test showing the candlepower distribution obtained from the lamp illustrated in Fig. 1. On this test has been plotted the results obtained from the refractor part only and the results obtained from the shade only. In this figure, 2| is the light distribution given by the complete lamp at angles below the horizontal. 22 is the light distribution given by the complete lamp at angles above the horizontal. This portion of the curve 22 is not always prodistribution 3| is obtained and the desk is well vided but is useful when an additional semiindirect lighting effect is desired by means of light reflected from the ceiling. The distribution of light'given by the refractor i5 alone is shown at 23. By subtracting this refractor distribution from the complete distribution curve 2|, curve 24 is obtained, which shows the light distribution given by the shade alone. From the foregoing it will be apparent that the dominant portion of -the downward component of light from the luminair is directed outwardly by the light-director at as wide an angle from nadir as possible below the shade for illuminating remote areas, and that the shade directs light, which it receives, down below the dominant rays from the light-director to illuminate areas adjacent nadir.

It will be clear that the refractor i5 gives a wide distribution of light, the maximum being at about 55 from the nadir. As the intense rays are directed outwardly at such wide angles from nadir, one can mount the light-director at a reasonably low elevation and effectively illuminate areas at a considerable distance from the axis of the luminair, whereby adequate light flux is available in the region eighteen inches or more from the lamp axis normally occupied when one is reading. Diflusion from the outer shade gives the curve shown at 24, which is produced by light transmitted through the refractor and reflector and striking the shade, and reflected in a generally downward direction.

The curve 25 of Fig. 2 is a fragment of a typical photometric curve showing only the distribution of light below an ordinary desk lamp having an upwardly opening hemispherical diffusing bowl and shade.

Fig. 3 shows what is obtained when the photometric curves are translated into illumination on a desk. The curves show the illumination in foot-candles at various distances from the axis of the lamp. The distribution of illumination obtained with the complete lamp is indicated at 3|. This is the light given by curve 2| of Fig. 2. The distribution of illumination given by the refractor is indicated at 33. This is the illumination produced by curve 23 of Fig. 2. The distribution of illumination given by the shade alone is indicated at 34. This is the light obtained from curve 24 of Fig. 2. It will be clear that the illumination on the desk close to the lamp is obtained largely by diffuse reflection from the shade and the illumination at a greater distance from the lamp is obtained largely by'the wide distribution given by the refractor. When these two are added together, a smooth light lighted over a wide area.

The distribution of illumination from a lamp whose photometric curve is such as shown at 25, is indicated at 35. The illumination tends to be excessive near the base of the lamp where it is least. needed and inadequate a short distance away where it is most needed. To help this condition, such lamps have been usually designed to place the bowl and shade at a considerable height above the desk. This helps the spread only a little, however, but is undesirable from the standpoints of appearance and adequate shielding of the interior equipment from the eyes. The curve 35 of Fig. 3 is the foot candle curve of illumination from such a lamp having the comparatively great height of 19 inches to bottom of shade, while curve 3| is the result with the new redirecting type of lamp at a height of only 15 inches to bottom of shade. The advantage of the redirecting type of lamp herein described is not only in the wide light distribution on the desk, shown at 3| of Fig. 3, but also in the lower height of lamp above the desk which. is of great advantage in appearance and in shielding the interior light-director from direct view of the worker.

The most important working area on adesk is usually from one to two feet out from the lamp. This is the area between the lines 36 and 31 of Fig. 3. It is impractical to light this area adequately and evenly by diffuse reflection alone, as indicated by the unsatisfactory distribution of curve 34. Plenty of light can be placed in this area by refraction from the refractor, as

indicated by curve 33. Itwould be possible to obtain a Wide, smooth distribution like 3| by means of a refractor alone. That is not desirable in this case. The refractor or light director is purposely designed to give an uneven distribution, with low illumination components close to the lamp and high illumination components at a distance from the lamp as shown by curve 33. The combination 3| of curves 33 and 34 has certain advantages which will be pointed out below.

Fig. 4 indicates this general idea of zones in which various brightness limits are desirable. The brightness limits given in this figure are arbitrary but indicate relatively and approximately the requirements of low brightness in a desk luminair. There is a certain zone of narrow angles from nadir out to approximately 35, in which the brightness should be relatively low because of the possibility of annoying specular reflections. There is another zone from this angle of about 35 up to approximately 75, or the lowest angle at which the lamp is likely to be viewed directly, in which a higher brightness is permissible. This is fortunate since, higher brightness accompanies the higher candlepower which is necessary to light the desk satisfactorily with a light-directing article, such as a refractor. Above this angle of approximately 75 and up to the highest point at which the lamp is likely to be viewed directly by anyone standing in a room, the brightness of the lamp should be very low. This limiting angle is indicated at 110 in Fig. 4. Above this angle there is no limit to permissible brightness since the light goes to the ceiling and only reaches the eyes after reflection from the diffuse ceiling surface.

By the combination of a powerful light-director in the form of a refractor and a shade white inside to produce a soft diffusing effect, the requirements' of desk lighting are met. Close to the lamp the larger part of the illumination on the working plane is obtained from. the diffusely reflecting shade, while the smaller part is obtained from the refractor. The brightness is low at these angles because the shade is large in area and the refractor is low in candlepower. At a distance of 1 ft. from the lamp and beyond, the larger part of the illumination is obtained from the refractor. The shade could not spread the light far enough to give satisfactory illumination on the desk at these distant points, and the higher brightness of the refractor is not objectionable at these higher angles. Many variations are possible in this general design and the invention is not confined to the particular lamp illustrated in Fig. 1. I

The reflector portion of the light-director as illustrated at IS in Fig. 1 is not a necessary part of the construction. It is here shown because it is ordinarily desirable, in order to reflect light to the ceiling and provide in the room a semiindirect effect in addition to the desk or reading light obtained from the refractor part. The light-director 40 of Fig. 4a has a lower prismatic refracting portion M similar to the lower portion l5 of the light-director of Fig. 1, and an upper spherical portion 42 of a shape to return light back through the lamp bulb and lower refractor portion, thereby increasing the intensity of the downward component of light from. the complete luminair.

The lower part of the light-director, which is 4 the refractor IS in Fig. 1, need not necessarily be a refractor. Any means which controls light accurately and condenses it into a beam to give a light distribution similar to 23 of Fig. 2 can be used. For example, a specular reflector will do this work although ordinarily such a construction is not quite as satisfactory as the refractor shown in Fig. 1.

. Fig. 5 shows a lamp embodying the general idea of this invention and using a reflector instead of a refractor for distributing the light widely over the desk. In this figure, M is the light center of the lamp. 62 is the lightdirector, of which 63 is a reflector sending light to the ceiling, and 6t is a reflector distributing light over the-desk. 65 is a diffusely reflecting shade. Light, ray 66 from the light center strikes the reflector and is reflected specularly as ray 51 at a relatively high angle from the nadir, so as to spread the light far out over the desk. Light ray 68 from the light center is similarly reflected and spread out over the desk as indicated at 69. Either reflector portion 63 or reflector portion 64, or both, may be translucent totransmit light for illuminating the shade 65. In this construction, it maybe desirable to make the reflector deep so that the desk will be shielded from the high brightness of the light source at low angles. A suitable diffusing shield 10 may be used to provide low brightness toward the desk at these low angles.

Since a desk lamp should always be placed at the left-hand side of the work (for right-handed workers), it is sometimes desirable from the standpoint of efliciency, to provide an asymmetric light distribution on the desk. Asymmetry may also be introduced into a lamp of this character and of the same general design as shown in Fig.1 by making the rei'raotor portion asymmetric. Thus in Figs. 6 and 7, the refractor portion of the light-director l5 could carry horizontal retracting prisms on its outer surface and vertical refracting prisms 9| on its inner surface. These vertical retracting prisms would redistribute the light sideways or laterally and so give an asymmetric distribution to the light which is delivered by the refractor to the desk.

What is claimed is: i

'1. Means for controlling the distribution of light from a source onto a plane surface, which comprises a light-directing appliance of small area adjacent the normal to the surface and disposed to direct light away from the normal to the.

surface and divert light from angles near nadir to angles remote from nadir whereby the brightness of such appliance is such that specular reflections thereof efiected at said surface and at angles near the normal have lower brightness than those at more remote angles, and a diffusing light-reflecting shade of larger area and of low surface brightness and disposed about the lightdirecting appliance for diffusely reflecting light toward such area to build up the intensity of illumination in said closer area whereby specular reflections of said shade at said surface have low beams at substantial angles to the axis for illuminating remote areas transverse of said axis, the

larger diameter portion having external reflecting prisms for reflecting light out through the mouth of the bowl, and a conical shade having a highly reflective inner surface placed about the bowl to intercept and diflusely reflect scattered light passing through the bowl, the reflected light from the shade being directed toward the axis.

4. A luminair for desk lighting having a light source disposed above the desk surface, a lightdirector about the source directing light out from nadir far enough to illuminate that portion of the desk which is at a normal reading distance from the luminair, and a highly reflecting shade about the light-director receiving transmitted light therefrom and directing such light toward that portion of the desk which is close to the luminair, the light-director being prismatic and having an upper reflecting portion and a lower portion provided with annular prisms for condensing downwardly emitted light in vertical planes and opposed vertical prisms for condensing it in horizontal planes to produce an asymmetric distribution of the direct light.

5. A luminair comprising a light source, an intensifying light-director about the light source, and a highly reflecting shade about the lightdirector, the light-director directing a dominant portion of the downward component of light of the luminair outwardly below the shade at a wide angle from nadir for illuminating areas below the shade and remote from nadir, the shade receiving other light rays transmitted by the light-director and being disposed at such an angle thereto as to direct such light downwardly below the dominantrays from the light-director and illuminate areas adjacent to nadir.

6. A luminair comprising a light source, a

light-director about the light source, and a highly reflecting shade about the light-director, the light-director including a refractor for directing a dominant portion of the downward component of light of the luminair outwardly below the shade at a wide angle from nadir for illuminating areas below the shade and remote from nadir, the shade receiving scattered light rays transmitted by the light-director and being disposed at such an angle thereto as to direct such light downwardly-below the. dominant rays from the light-director and illuminate areas adjacent to nadir.

7. A luminair comprising a light source, a lightdirectd-v about the light source, and a highly reflecting shade about the light-director, the lightdirector including a reflector for directing a dominant portion of the downward component of light of the luminair outwardly below the shade at a wide angle from nadir for illuminating areas beiii? low the shade and remote from nadir, the shade receiving other light rays transmitted by the lightdirector and being disposed at such an angle thereto as to direct such light downwardly below the dominant rays from the light-director and illuminate areas adjacent to nadir.

8. A luminair comprising a light source, an intensifying translucent light-director about the light source, and a highly reflecting shade about the light-director, the light-director having a lower part for directing a dominant portion of the downwardly emitted light outwardly below the shade at a wide angle from nadir for illuminating areas below the shade and remote from nadir and an upper part for reflecting light upwardly, the shade receiving light rays transmitted by both parts of the light-director and being disposed at such an angle thereto as to direct such light downwardly below the dominant rays from the light-director and illuminate areas adjacent to nadir.

9. A luminair comprising a light source, a translucent light-director about the light source, and a highly reflecting shade about the light-director, the light-director having a lower light refracting part for directing a dominant portion of the downwardly emitted light outwardly below the shade at a wide angle from nadir for illuminating areas below the shade and remote from nadir and an upper part for reflecting light upwardly, the shade receiving light rays transmitted by both parts of the light-director and being disposed at such an angle thereto as to direct such light downwardly below the dominant rays from the light-director and illuminate areas adjacent to nadir.

10. A luminair comprising a light source, a translucent light-director about the light source, and a highly reflecting shade about the lightdirector, the light-director having a lower inverted reflecting bowl for directing a dominant portion of the downwardly emitted light outwardly below the shade at a wide angle from nadir for illuminating areas below the shade and remote from nadir and an upper part for reflecting light upwardly, the shade receiving light rays transmitted by both parts of the lightdirector and being disposed at such an angle thereto as to direct such light downwardly below the dominant rays from the'light-director and illuminate areas adjacent to nadir.

11. A luminair comprising a light source, a prismatic light-director about the light source, and a highly reflecting shade about the lightdirector, the lower portion of the light-director refracting the light so that a dominant portion of the downwardly emitted light is directed outwardly below the shade at a wide angle from nadir for illuminating areas below the shade and remote from nadir, the upper part of the light-director reflecting light upwardly for an indirect component of illumination, the shade receiving other light rays transmitted by the light-director and being disposed at such an angle thereto as to direct such light downwardly below the dominant rays from the light-director and illuminate areas adjacent to nadir.

12. A luminair for desk lighting having a light source disposed above the desk surface, a translucent light-director about the source, and a shade about the light-director, the light-director acting on downward components of light to direct an intense beam of light below the shade and out from nadir to illuminate that portion of the desk which is at a normal reading distance from the luminair, the shade being highly reflecting and receiving transmitted light from the lightdirector and directing such light toward that portion of thedesk which is close to the luminair, the light-director having a reflector portion to send some light to the ceiling.

13. A luminair for desk lighting having a light source disposed above the desk surface, a bowlshaped, prismatic light-director about the source, and a shade about the light-director, the lightdirector including a lower refracting portion and an upper reflecting portion, the lower portion acting on downward components of light to direct an intense beam of light below the shade and out from nadir to illuminate that portion of the desk which is at a normal reading distance from the luminair, at least one portion having vertical prisms for condensing light in horizontal planes to produce an asymmetric distribution of light, the shade being highly reflecting and receiving transmitted light from the light-director and directing such light toward that portion of the-desk which is close to the luminair. r

THOMAS W. ROLPH. 

